The present invention relates to a radiation-curable organopolysiloxane composition or, more particularly, to a radiation-curable organopolysiloxane composition which, when cured by irradiation on a substrate, such as a plastic film, forms a cured surface film having excellent adhesive bonding strength to the substrate surface and is capable of exhibiting excellent releasability from sticky substances.
Various types of radiation-curable organopolysiloxane compositions are known in the prior art. Those of a typical class comprise an organopolysiloxane having (meth)acryloxy, i.e. acryloxy and/or methacryloxy, groups in the molecule, and examples are found, for example, in Japanese Patent Kokai 48-48000, 63-135426, 2-45532 and 2-163166 and elsewhere. One of the important applications of these radiation-curable organopolysiloxane compositions is as a surface-treatment coating agent on various kinds of substrate surfaces such as the back surface of pressure-sensitive adhesive tapes, temporary protecting sheets for pressure-sensitive adhesive labels and the like by virtue of the excellent releasability from sticky substances exhibited by the cured film of the composition.
It is a trend in recent years that the bonding work for attaching these pressure-sensitive adhesive tapes or labels to the surface of a substrate is conducted at a high speed by using a machine with rapid rewinding of the adhesive tape from a roll or by peeling the temporary protecting releasable sheet off from the adhesive surface of the labels. A problem in such a bonding work is that, when the sticky adhesive surface coated with a pressure-sensitive adhesive and the releasable surface having a cured film of the organopolysiloxane composition are separated at a high speed, a noise, called a peeling noise, is unavoidably generated, which is sometimes so high as to cause deterioration of the working environments.
Generation of the above mentioned peeling noise means, in an aspect, that the resistance against peeling to separate the adhesive surface and the releasable surface is under uncontrollable fluctuation in a range so large that the machine-bonding works of the pressure-sensitive adhesive tapes or labels, which must desirably be conducted under a constant peeling resistance, is greatly affected thereby to cause inaccuracy in the attaching position of the tapes or labels. It is empirically known that the peeling noise is generated when the peeling resistance exceeds a certain level so that it is eagerly desired to develop an organopolysiloxane-based releasing agent which is free from generation of any peeling noise irrespective of the peeling resistance.